HP 8753D Option 011 User Manual

Since the
chosen
VCO
harmonic and
the source
dier
b
y
0.500
or
0.333
MHz,
then
another
V
CO
harmonic,
2
or
3
times
higher
in
frequency
,
will
be
exactly 1.000
MHz a
wa
yfrom
the
2nd
or
3rd
harmonic of
the source
frequency.
The samplers,
then, will
also do
wn-conv
ert
these
harmonics to
yield the
desired
comp
onen
ts
in
the
1st
IF
at
1.000
MHz.
Narrow
bandpass
lters
in
the
receiv
er
eliminate
all but
the 1.000
MHz signals;
these pass
through to
be
pro
cessed and
display
ed.
Figure
HARBLK12
here.
Figure
12-6.
Harmonic
Analysis
External
Source Mode
In
external source
mo
de,
the
analyzer
phase
lo
c
ks
its
receiv
er
to
an
external
signal
source.
This
source
m
ust
b
e
CW (not
swept),
but
it
do
es
not
need
to
b
e
syn
thesized.
The
user
m
ust
en
ter
the
source
frequency
in
to
the
analyzer.
(The
analyzer's
internal
source output
is not
used.)
T
o
accomplish
this,
the
phase
lo
c
k
lo
op
is
reconnected
so
that
the
tuning
v
oltage from
the
A11 phase
lo c
k assem
bly con
trols
the
V
CO
of
the
A14
fractional-N
assem
bly
and
not
the
A3
source.
See
Figure
12-7
.
The
VCO's
output still
drives
the 1st
LO
of
the
samplers
and
do
wn-con
v
erts
the
RF
signal
supplied
b
y
the
external
source. The
resulting 1st
IF is
fed bac
k
to the A11 phase lo c
k assem
bly, compared
to the 1.000 MHz reference, and used to generate
a
tuning v
oltage as usual. Ho
wever, the tuning v
oltage con
trols the V
CO to lo c
k on to the
external source, k
eeping the 1st IF at exactly 1.000 MHz.
The analyzer normally go es through a pretune-acquire-trac
k sequence to ac
hiev
ephase
lo c
k.
In external source mo de, the fractional-N V
CO pretunes as a closed-lo op syn
thesizer
referenced to the 100 kHz signal from the A12 reference assem
bly. Then, to acquire or trac
k,
a switc
h causes the V
CO
to be tuned b
y the A11 phase lo c
kassem
bly instead. (Refer to the
Overall Blo ck Diagram at the end of Chapter 4, \Start Troublesho oting Here.")
12-16 Theory of Operation DRAFT
3/21/106 15:14
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HP 8753D Option 011 Specifications

General

Brand	HP
Model	8753D Option 011
Category	Measuring Instruments
Language	English